Centimeter wave apparatus



Sept. 9, 1947. v. D. LANDON CENTIMET'ER WAVE APPARATUS Filed Oct. 29, 1945 En" s:

v:Snvcutol' N DLANDUN VERN @M e? H5 Gttorlug Patented Sept. 9, 17947 2,427,107 CENTTMETER WAVE APPARATUS Vernon D. Landon, Princeton,

N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 29, i943, Serial No. 508,229

Claims.

This invention relates generally to centimeter wave apparatus and more particularly to an improved method of and means for tuning and coupling in waveguide microwave transmission systems.

I-Ieretofore, waveguide transmission systems and cavity resonators have been tuned by means of micrometer operated tuning plungers or by means of various types of tuning screws. One of the principal disadvantages in tuning systemsof these types is that erratic Contact inherent in all screw-fed or sliding contact devices provides a variable contact resistance which is especially objectionable wherever high microwave current values occur. Since the sliding Contact or threaded joint in many known devices is situated adjacent to the waveguide walls, it will be seen that this location coincides with conditions of high microwave currents.

The instant invention contemplates a tuning.

screw which may be employed either for tuning a resonant cavity or waveguide or for providing adjustable coupling between two such devices. The proportions of the apparatus to be described -ereinafter are such that the region of coincidence of the tuning screw or coupling element with the adjacent wall of the waveguide or resonant cavity is maintained substantially at ground potential. Furthermore, the device is proportioned so that all threaded or sliding contacts occur at regions of minimum microwave currents whereby contact resistance variations do not introduce objectionable variations in the current distribution in the conductors.

The features of the instant invention mentioned heretofore are accomplished by providing a supporting structure for the tuning screw or coupling element which forms a concentric line therewith having a length of the order of any predetermined multiple of 1/2 wavelength at the operating microwave frequency. The contact points between the supporting element and the tuning screw or coupling element are permitted to touch the tuning screw or coupling element only at points disposed distances of the order of odd multiples of 1A wavelength at the l operating microwave frequency from the ends of the half wave concentric line. Preferably, the contact means include flexible contact elements providing low resistance joints. Supplemental threaded means may be included with one or more of the contact elements to provide convenient screw feed for the movable element.

One of the embodiments of the invention to (Cl. ri- 44) 2 resonator. Another embodiment of the `invention, also to be described hereinafter, comprises be described hereinafter comprises an improved tuning screw for tuning a waveguide or cavity an improved adjustable coupling device for coupling microwave energy from a cavity resonator to a waveguide transmission system. Both of the embodiments utilize substantially the same means for providing movable electrical contacts at points of minimum microwave current distribution.

Among the objects of the invention `are to provide an improved method of and means for reactively coupling to a microwave transmission system. Another object of the invention is to provide an improved method of and means for tuning a microwave transmission system. An additional object of the invention is to provide an improved tuning screw for a waveguide transmission systemwherein the movable contacts are disposed at points of minimum microwave current distribution. A further object of the invention isto provide an improved method of andmeans for providingfixed microwave coupling to a cavity resonator and providing adjustable microwave coupling between said resonator and a waveguide transmission system. A further object of the invention is to provide an improvedmethod of and means for tuning a microwave waveguide transmission system, introducing modulated microwaves to said system, providing variable coupling between a source of local oscillations and said waveguide transmission system, and mixing and detecting said modulated signals and said local oscillations to derive desired signal modulation components.

The invention will be further described by reference to the accompanying Vdrawing of which Figure 1 is an elevational cross-sectional view of the complete system including all of the embodiments thereof described hereinafter. Figure 2 is a schematic circuit' diagramV of the equivalent :electrical circuit of the complete system. Similar reference characters are applied to similar elements throughout the drawing.

Wave. detector the walls I vof a electrical contact between the detector terminal 1 and the waveguide wall I.

A silicon crystal I3 is electrically connected to and supported by a cylindrical projection I5 of the detector terminal 1. The crystal I3 has a knife edge I1 which engages a tungsten wire catwhisker I9. The tungsten wire cat- Whisker I9 is supported by a second cylindrical detector terminal 2|. The cylindrical conductive members I5, 2l, and the crystal I3 and catwhisker I9 are enclosed within a glass, ceramic or suitably insulated sleeve 23. A cylindrical prong 25 projects coaxially from the outer end of the second cylindrical supportingv member 2i. This type of microwave crystal detector is disclosed and claimed in a copending U. S,. application of William D. Larue, Serial No. 432,818 filed February 28, 1942, and assigned to the same assignee as the instant application.

The wall 21, of the waveguide 3, opposite the waveguide wall I, includes a threaded aperture for receiving a second threaded sleeve 29 which surrounds the prong 25 and the second cylindrical terminal 2 I. The penetration of the threaded sleeve 29 into the waveguide interior may be varied by rotation thereof in the threaded aperture in the waveguide wall 21. A flexible contact ring 3l, which may be suitably secured to the wall 21, provides uniform electrical contact between the second threaded sleeve 29. and the waveguide wall 21. If fixed filtering is. desired, the sleeve 29 may be fixed in position by soldering it to the waveguide Wall 21.

The second threaded sleeve 29 is terminated in an annular ring portion 33. A fiat plate 35 is separated from the annular ring 33 by a layer of mica, or other dielectric, 31. to provide a relatively large capacitor which is indicated in Figure 2` as the` capacitor C2. A terminal 39 provides an output connection to the flat plate 35 while a second terminal 4I and insulated bushing 43 provide an output terminal for the annular ring 3,3. A flexible cylindraceous contact element 4,5, electrically connected to the fiat plate 3 5 adjacent an aperture in the centerthereof, DrOVideS. a sliding electrical contact with the prong 25,. The cavity formed .between thefprong 25, the second threaded sleeve 29, and the flat plate 3,5.- may be proportioned to be substantially anti-resonant tothe microwave operating or carrier frequency.

It will be seen that the` effective inductance LI provided by the prong 25 and the flexible contact element 45 may be varied by rotating the entire capacitor supporting structure within the threaded aperture in the waveguide wall` 21. The effective bypassing of microwave signal components derived from. the detector-is accomplished by a capacitor providedbetween the inner surface of the second threaded sleeve 29 and the outer surface of the. conductive second cylindrical detector terminal 2|. This capacitor is CI- of Figure 2, and also may be effectively varied simultaneously with the inductance LI by rotating the second threaded sleeve 29-to project more or less of the sleeve 29 into the interior of the waveguide.

The output terminals 39, 4I may be connected to any desired modulation utilization circuit such as, for. example, the primary winding.rr 41 of an intermediate frequency transformer T I. It should be understood that modulated microwave signals and unrnodulated` local oscillations both may be introduced into the waveguideV 3 to provide intermediate frequency modulated4 signals at the 4 output terminals 39, li'i of the capacitor C2. The means for introducing and tuning the waveguide 3 to the source of modulated microwave frequencies, and means for introducing and adjustably coupling the source of local oscillations to the waveguide 3 will be described in detail hereinafter.

Operation The operation of the crystal detector is apparent from the schematic equivalent circuit diagram of the system illustrated in Figure 2. The crystal detector 9 is illustrated as interposed in series between an impedance Z0, representing the waveguide characteristic impedance, and an impedance ZI, representing the output load impedance. The variable capacitor Cl, connected between the load terminal of the crystal and the common terminals of the waveguide and load impedances, represents the main bypass capacitor for the microwave signal components passing through the crystal detector. The variable inductive element LI, corresponding to the inductance interposed by the center prong and contacts 25, 45 is effectively connected in series with the crystal and one terminal of the load impedance Z'I. The capacitor C2 is effectively connected directly across the load impedance ZI. The dash line 49 is indicative of the fact that the capacitor CI and the inductor LI are adjustable simultaneously. It will be seen that the network effectively connected between the crystal detector and the load impedance ZI represents a low-pass filter having a relatively large bypass capacitor CI on the input thereof for bypassing the microwave signal components. The Q of the filter network is. relatively high, since the network elements are essentially pure reactances. The wave detector system thus disclosed is described and claimed in a copending U. S. application of Wendell L. Carlson, Serial No. 501,755, filed October` 26, 1943, entitled Centimeter wave detector, and is assigned to the same assignee as the instant application.

Tuning screws Again referring to Figure 1, the waveguide 3 is terminated at one end by a conductive plate 5 I. The resultant resonant cavity 53 may be tuned by one or more tuning screws 55, 51 to resonate at either themodulated signal carrier frequency, the local oscillator frequency or the mean frequency of the carrier and local oscillation frequencies. All tuning screws may be identical and may be spaced predetermined fractions of the operating wavelengths.

'I he tuning screw 5,1 therefore maybe taken as typical. ItI comprises a cylindrical supporting shelllI having` one end secured to and surroundingan aperture 63 in the wall I. of the waveguide 3. rIfheV supporting shell (ily forms a half wave concentric line withy the tuning screw element 65 which is disposed. coaxially therewith. The length of the conductive shell 6I may be any predetermined multiple of- 1/2 wavelength at the operating frequency. Clearance is provided between. the tuning screw. 65 and the supporting shellY lI` except at points removed any predetermined odd multiples of 1A; wavelength from the ends ofr the supporting shell 6I.. At such protruding and reentrant points, the supporting shell includes exible contact elements 61, 69

whichprovide electr-ical contact between the supporting shell and the tuning screw at current nodes or points ofv minimum microwave circulating currents. The protruding contacts 69 may include threaded portions which engage complementary threads 'H in the exterior portion of the tuning screw 65. An adjusting knob 'I3 may be keyed to the outer end of the tuning screw 65 by means of a key 15. The inner end of the tuning screw 65 may include an enlarged cylindrical portion 'Il having a diameter providing ample clearance with the supporting shell 6| and the aperture in the waveguide wall I. The length of the enlarged cylindrical end of the tuning screw 65 may be of the order of 1A; wavelength, or any odd multiple thereof, depending upon the proportions of the supporting shell and the reentrant portion thereof.

It will be seen that the half wave line provided by the supporting shell 6l and the tuning screw 65, 11 provides a point of substantially ground potential in the region of the waveguide aperture. Furthermore, the points of contact of the iiexible contacts 61, 69 on the surface of the tuning screw E are at multiples of M1 wavelength from the point of ground potential and correspond to regions of minimum microwave current.

Variable microwave coupler A source of oscillations derived from, for example, the output line 79 of a Shepard tube oscillator 8i supported on the end terminating plate 5l of the waveguide 3, is introduced into a cavity resonator or concentric line 83 which comprises an outer conductive wall 85 and an inner movable cylindrical rod 81. Shepard oscillator tubes are representative of the well known type of microwave generators having a thermionic cathode and a negatively biased reflector electrode housed within a cavity resonator. Tuning of the cavity resonator, for example, by distortion of the resonator walls, varies the output frequency. .Output energy is derived from a short coaxial output line coupled to the resonator. The length of the cavity resonator 83 is selected to be of the order of any multiple of 1/2 wavelength at the oscillator frequency. A reentrant portion 89 of the cavity resonator 83 includes flexible contacts 9i which engage the cylindrical central rod 8l at a point removed substantially 1A. wavelength from either end of the cavity resonator 83. A protruding portion 93 of the cavity resonator 83 may be of the order of 1/2 wavelength at the oscillator frequency. At a point 1A; wavelength removed from the end of the cavity resonator 33, a second flexible contact 35 engages the shank of the cylindrical rod 31. The remainder of the protruding portion 93 of the cavity resonator 83 may be threaded to engage complementary threads in the output portion of the cylindrical rod 8l. A third control knob 91 may be keyed by means of a key 93 to the outer end of the cylindrical rod 8l. The waveguide wall l is apertured to provide clearance for the cylindrical rod 8l whereby the inner end of the rod may be introduced into the interior of the waveguide 3. The degree of penetration of the inner end of the cylindrical rod S1 into the waveguide 3 may be adjusted by rotating the third control knob 97. As illustrated, the spacing between the cylindrical rod 81 and the output line 79 of lche Shepard tube 3l remains fixed, thereby providing fixed capacitive coupling between these elements. It will be seen that the coupling from the Shepard tube 8| to the waveguide 3 and the crystal detector 9 may, therefore, be adjusted readily by rotating the third control knob 91.

Referring again to Figure 2, the operation of the complete system may be defined as follows. Modulated microwave signals having a carrier frequency fl -may be introduced into the waveguide 3 in any known manner effectively across thewaveguide characteristic impedance Z0. The tuning screws 55, 51 are represented by the variable impedance Z2, effectively connected in shunt with the characteristic impedance ZD. The Shepard tube local oscillator` provides a local microwave energy source havinga frequency f2. The variable coupling between the Shepard tube and the waveguide is denoted by the series connected variable impedance Z3 while the Shepard tube is represented lby the impedance Z4. The crystal detector with its lter network CI, C2, Ll provides effective bypassing of the microwave components fl, f2 and fbi-f2 and provides a modulated intermediate frequency signal fl-f2 across the load impedance ZI.

It should be understood that the tuning screws and the adjustable microwave coupler may be employed in any other manner known in the microwave art, and that the particular proportions thereof disclosed herein may be employed in other types of microwave apparatus wherein the adjustment of reactive circuit elements involves movable electrical contact between conductive circuit elements.

Thus the invention described comprises several modications of improved reactive circuit elements wherein erratic contact effects are substantially overcome by locating the movable contacts in the region of microwave current nodes. An improved tuning screw, a variable microwave coupler and a complete system including a microwave converter have been described in combination with said tuning screws and coupler.

I claim as my invention:

1. Microwave apparatus for a waveguide transmission system including a threaded screw member, support means engaging said screw member for introducing said screw member through an apertured waveguide wall, said member and said means being proportioned with respect to the operating frequency and engaging at a predetermined distance from said apertured wave guide wall t0 maintain the portion of said member in the immediate region of said waveguide aperture substantially at ground potential, and contact'means interconnecting said member and said support means and providing said engaging means for said threaded portion of said member at a current node on said member.

2. A microwave coupling device including a resonant concentric line comprising a threaded screw member, conductive support means engaging said screw member concentric with respect to said member for introducing said member through an apertured waveguide wall, said member and said means being proportioned with respect to the operating frequency and engaging at a predetermined distance from said apertured waveguide wall to maintain the portion of said member in the immediate region of said waveguide aperture substantially at ground potential, and contact means providing said engaging means interconnecting said member and said support means at current nodes on said member, means for .coupling a source of microwave energy to said line,- and` means for adjusting the penetration of said-member through said waveguide aperture for varying the microwave coupling to said waveguide.` Y

3. A microwave coupling device including a waveguide having an aperturedwall, a resonant 2am-rev concentric line lcomprising .a lthreaded .fscrew member,rconductivesupportmeansfengaging;said screw `member :mounted .upon said @wall :adjacent said aperturezand concentricwith respectltasaid member for introducing said :member through said apertured lwaveguide iwall, saidzmemberfand said means being :proportioned with respect to the .operating .frequency .and y:engaging .at a predetermined ;distance from said fapertured :Waveguide wall lto imairitain the zportion fof said member in the immediate region of :said :waveguide aperture substantially :at ground potential, .fand Contact means `providing said kengaging .means interconnecting said :member land '.sa'id fsupport means .at current modes -ron sa'id fmember, 'means for :coupling microwave energy 'to said dine, tand means `for adjusting the penetration ci lsaid member .through -said waveguide :aperture vfor varying the microwave coupling to fsaid 'waveguide.

'4. A tuning screw for a rmicrowave iwaveguide including Ya :threaded :screw member, -isupport means engaging :said screw imember for `intrinducing said screw member-throughan apertured waveguide wall, :means '.proportionedwith :respect to .the operating frequency and fengaging at "a predetermined distance :from fsaid sapertured waveguide wall for maintaining ztlre :portion yof said screw :member fin `the immediate :region of said waveguide :aperture :substantially xat .ground potential, and :contact Vmeans lproviding :said `engaging .'means connecting said screw .'member and said support means .at current `nodes on vsaid tuning screw.

f5. A tuningscrew 'for amicrowavewaveguide including a threaded screw member, support means threaded to said screwimember for introducing said screw member through an apertured waveguide wall, means proportioned with respect to the operating frequency and vengaging at a predetermined :distance .from -said .-.apertured waveguide .wall for maintaining :the portion =of said screw memberin -the immediate .-regionfof said .waveguideaperture substantiallyat :ground potential, and contact means lproviding said engaging meansv connectingsaid screw-member and said support .means -at -current rnodes fon ,said tuning screw.

6. Microwave .apparatus for `tuning 1.a vwaveguide system comprising .a :waveguide vhaving v:an aperture mene-ofthe wallsthereoifand aftuning screwfoperable.through-said :wall aperture-to `tune said waveguide as. a function .of the Ipenetration of said tuning screw into said waveguide, means combined with said .tuning :screwiorming therewith a concentric line .having .a length of the order of .a predetermined .multiple of one half wavelength at the 'operating microwave .frequency, said means .having Ione :end thereof secured to said waveguide -and surrounding ysaid aperture, contacts .connecting `said tuning e screw and said means at points .of Lthe'orderof `.precietermined v.odd multiples 01E-one quarter wavelength from the .junction-of .said-.means =andsaid waveguide, :and vmeans -for rotating `said tuning screw to vary the .penetration .thereof .within said waveguide.

'7. Microwave .apparatus for tuning .-a waveguide system comprising a waveguidehavingfan aperture in one of the `walls thereof, and a .tuning screw including, in combinationfa `hollow cylindrical conductive elementhaving-.a length of `the order of a predetermined multiple of zone half Wavelengthatitheoperating-microwavezirequency andihavingoneend thereof 4.secured to said -waveguide andsurrounding said aperture, van apertured concentric .cylinder :having .a reentrant portionwandaprotruding portion each extending lengths .o'i 'the .order of :predetermined odd multiples :of Yone quarter wavelength coaxially from the .remaining endof saidelementand each being terminated .in flexible vcontact elements, .a threadedicylindraceous conductive member contacting said contact elements and coaxially spaced from the intermediate vportions of said concentric cylinder, -and .means 'Ifor Irotating said member to -vary the .penetration .of one end of said member .within said waveguide.

8. Microwave apparatus for tuning:a .waveguide systemcomprising a waveguide vhaving :an aperture in one of .the walls :thereof, and a tuning screw including, in combination, alhollow cylindrical conductive element having a 'length' of .the order :of one half wavelength at theoperating microwave frequencyzand having one endthereof .secured Eto said `waveguide and surrounding said aperture, a vhollow vconcentriccylinder having a reentrant .portion and a protruding portion each extending.lengthsofthe order of-one quarter wavelength coaxially from the remaining end of said el'ement-and-eachrbeing terminated 4in flexibleLcontact elements, a threadedfcylindraceous conductive mem-ber `contacting Ysaid lcontact -elements and coaxially vspaced Athereby from the intermediate [portions of lsaidconcentric cylinder, and means 'for rotating said member to varythe penetrationof one -end of said member within said waveguide.

9. -Microwave apparatus for tuning -a Waveguide system comprising a waveguide having an aperturein one'offtlie walls thereof, and a tuning screw including-incombination, a vhollow cylindrical conductive element having a llength of tileorderfof-onefhalf wavelength at the operating microwave -frequency and-having oneend'thereof secured to said waveguide and surrounding said aperture, an .apertured 4concentric cylinder havinga reentrantportion and a'protrudingportioneachextending lengths of 1theorder of one quarterwavelengthcoaxially from-the remaining endof said-element and'each beingterminated in flexible contact elements, a threaded cylindraceous conductive member-contactingsaidcontact elements andcoaxially spaced fromthe intermediate portions of said concentric cylinder, threaded vmeanscoaxial withsaid protruding concentric cylinder yportionengaging said threaded cylindraceous memben and lmeans Ifor rotating sai-d member to vary the 1penetrationof-onevend oi' =said ymember within said waveguide.

-10. .Apparatus of the type described in claim 3 including a wave detectorfdisposed in said waveguide, means for introducingenergy from a second .source of microwave energy into said waveguide, and means for deriving from-said detector currents having predetermined modulation componentsof said two sources of microwave energy.

VERNON D. LANDON.

TREFERENCES Y'CIllED UNITED STATES PATENTS Name Date Southworth l Sept. 13, 1938 Number 

